PIC controller based heater controller. It’s based around a pump controlled boiler/radiator system. A PIC16F84 is used to input the set point and control a pump to circulate the heated water as needed. source

This circuit will turn on/off 12V DC fan or CPU fan when temperature above preset temperature.You can set turn on temperature by adjust VR1. This circuit use an NTC (Negative temperature coefficient) as a temperature sensor.The NTC is a thermistor that the zero-power resistance decreased when  increase the temperature. source

This circuit use a single-supply system to precisely measure the temperature at a remote location with less than 1°C error over a 0 to 100°C range . The circuit includes a low-cost AD590 temperature sensor, an AD8541 rail-to-rail amplifier, four resistors, a trimming potentiometer and an ADC. source

Scriptable Thermometer is a A unified thermometric controller that can be programmed with simple scripts, integrating the “classic” thermometer/controller pair.source

The project helps you control two fan’s to cool whatever you need by adjust the trimpot. It works by cooling with the first fan when the sensor detects a user adjustable temperature, and it turns the second fan on, when the temperature exceeds 5 degrees over the user adjusted temperature.Each fan turns off when the temperature drops 5 degrees below its turn-on temperature. For example, if the trimpot is set to 80 degrees, the fan turns on at 80 degrees and turns off at 75 degrees.The circuit controlled by ATtiny45.source